1. Field of the Invention
This invention relates to terrain navigation apparatus for effecting terrain navigation of a legged animal traversing terrain.
2. Discussion of Prior Art
There are a number of navigation aiding sources currently in use in the open field or similar environments. These include magnetic heading, for deducing true heading; magnetic heading and pedometer, for performing dead-reckoning; magnetic heading for performing a running a fix on a landmark, thereby enabling computation of position; transit on two landmarks or on-top fix on landmark, which enables correction of position errors; GPS and JTIDS fix, for correcting position errors; barometric height update, for correcting height errors; and feature fix for correction of position and height, where knowledge of certain terrain features may be used for position and height updates, e.g. crossing a known section of straight road enables correction of position errors in a direction orthogonal to the road even though the crossing point is not fully defined, and crossing a known saddle point enables correction of height.
However, difficulties have arisen in difficult environments due to effects such as interference or jamming suppressing GPS, magnetic influences disturbing magnetic compasses, difficult or variable terrain leading to pedometer errors, and poor visibility affecting map-reading or sighting on land-marks. These problems are all characterised by discontinuities in available sensor or aiding information. These discontinuities can occur at critical times and are thus extremely undesirable.
Recent advances in Inertial Navigation Units (INU) have led to smaller and smaller units being produced. These may be based on Fibre Optic Gyroscope (FOG) technology, but they are still comparatively expensive. An INU may be integrated with some or all of the additional aiding sources described above, potentially enabling the above-mentioned gaps in data associated with the aiding sources to be bridged. However the drawback is partly the size of the FOG INU, and partly the cost. Recent advances in silicon gyro technology have led to gyros that can be produced on silicon production lines. This has the advantages of small size, mass production and low cost. However the gyro performance is at the low end for INU operation. These gyros, and similarly silicon accelerometers, provide the basis for a low performance INU, providing autonomous free-navigation that is only useful for very short periods of time.
There is therefore a need for a generally improved system for effecting terrain navigation in the open field that can make use of small size, low cost gyroscopes, in conjunction with a system performance enhancement that will give adequate performance over typical field operations and conditions.
According to a first aspect of the present invention there is provided terrain navigation apparatus for a legged animal traversing terrain including a first system for determining position, velocity and heading of the legged animal incorporating sensing means for sensing inertial motion in six degrees of freedom operable to provide signals indicative of a first velocity, a first heading and a first position of the legged animal, contact means for establishing, in a velocity profile describing motion of either foot of the legged animal, a period where the velocity should be zero, which period corresponds to full or partial contact of the respective foot with surrounding terrain, and error-estimating means for receiving as input signals the velocity profile during the period and for providing as output signals estimates of errors associated with the sensing means output signals, which errors operatively interact with the output signals of the first system to effect terrain navigation of the legged animal.
Preferably the legged animal is a human being.
Conveniently the sensing means include three mutually orthogonal specific force sensors and three mutually orthogonal angular rate sensors.
Advantageously the contact means is a matched filter arrangement.
Preferably the contact means is a pressure switch arrangement.
Conveniently the velocity profile is the first velocity output from the first system.
Advantageously the error-estimating means includes a Kalman Filter.
Preferably there is provided heading means for determining true heading of the legged animal, which heading means is in operative association with the first system.
Conveniently the heading means is a magnetic compass operable to output a magnetic heading.
Advantageously there is provided a satellite radio-navigation system, which satellite radio-navigation system is in operative association with the first system.
Preferably the satellite radio-navigation system is a Global Positioning System (GPS) operable to output a GPS position and a GPS velocity.
Conveniently the first system is locatable on a lower leg region of the legged animal.
Advantageously the first system is locatable on a foot of the legged animal.
Preferably there are two first systems, each locatable on a lower leg region of one leg of the legged animal.
Conveniently the first system is locatable at a lower back region of the legged animal.
Advantageously there is provided including a second system for determining position, velocity and heading of the legged animal incorporating sensing means for sensing inertial motion in six degrees of freedom operable to provide signals indicative of a second velocity, a second heading and a second position of the legged animal.
Preferably the second system is locatable on a lower leg region of the legged animal.
Conveniently the second system is locatable on a foot of the legged animal.
Advantageously there are two second systems, each locatable on a lower leg region of one leg of the legged animal.
Conveniently there is provided a position summation station for combining the first position and second position when the same have been corrected by the errors estimated by the error-estimating means, to provide a position difference, which position difference is thence received as input to the error-estimating means.
The present invention is suitable for use with any legged animal which moves across terrain by contacting the terrain by feet, hooves, skis or the like on its legs, such as a human being, and for convenience in the following description a legged animal will be referred to as a man.